Transmissive image modulator using multi-fabry-perot resonant mode and multi-absorption mode

Abstract

A transmissive image modulator for allowing image modulation over a wide bandwidth with multiple Fabry-Perot resonant modes and multiple absorption modes is provided. The transmissive image modulator includes a lower reflection layer; an active layer disposed on the lower reflection layer, including multiple quantum well layers and multiple barrier layers; an upper reflection layer disposed on the active layer; and at least one micro-cavity layer disposed in at least one of the lower and upper reflection layer. The active layer and the at least one micro-cavity layer have thicknesses of a multiple of λ/2, where λ is a resonant wavelength.

What is claimed is: 
     
         1 . A transmissive image modulator comprising,
 a lower reflection layer;   an active layer disposed on the lower reflection layer, the active layer comprising a plurality of quantum well layers and a plurality of barrier layers;   an upper reflection layer disposed on the active layer; and   at least one micro-cavity layer disposed in at least one of the lower and upper reflection layer,   wherein the active layer has an optical thickness which is a multiple of λ/2, and the at least one micro-cavity layer has an optical thickness which is a multiple of λ/2, where λ is a resonant wavelength.   
     
     
         2 . The transmissive image modulator of  claim 1 ,
 wherein each of the lower reflection layer and the upper reflection layer is a DBR layer comprising first refractive index layers and second refractive index layers stacked alternately, wherein a first refractive index of the first refractive index layers is different from a second refractive index of the second refractive index layers, and wherein each of the first refractive index layers and each of the second refractive index layers has a thickness of λ/4.   
     
     
         3 . The transmissive image modulator of  claim 2 ,
 wherein the lower reflection layer comprises a first lower reflection layer, a first micro-cavity layer disposed on the first lower reflection layer, a first phase matching layer disposed on the first micro-cavity layer, and a second lower reflection layer disposed on the first phase matching layer.   
     
     
         4 . The transmissive image modulator of  claim 3 , wherein:
 the first lower reflection layer comprises first pairs of the first and second refractive index layers,   the first micro-cavity layer comprises the first refractive index layer,   the first phase matching layer comprises the second refractive index layer, and   the second lower reflection layer comprises second pairs of the first and second reflective layers.   
     
     
         5 . The transmissive image modulator of  claim 4 ,
 wherein a number of the first pairs is less than a number of the second pairs.   
     
     
         6 . The transmissive image modulator of  claim 3 ,
 wherein the upper reflection layer comprises a first upper reflection layer, a second phase matching layer disposed on the first upper reflection layer, a second micro-cavity layer disposed on the second phase matching layer, and a second upper reflection layer disposed on the second micro-cavity layer.   
     
     
         7 . The transmissive image modulator of  claim 6 , wherein:
 the first upper reflection layer comprises third pairs of the first and second refractive index layers,   the second phase matching layer comprises the second refractive index layer,   the second micro-cavity layer comprises the first refractive index layer, and   the second upper reflection layer comprises fourth pairs of the first and second reflective layers.   
     
     
         8 . The transmissive image modulator of  claim 7 ,
 wherein a number of the third pairs are larger than a number of the fourth pairs.   
     
     
         9 . The transmissive image modulator of  claim 6 ,
 wherein the lower and upper reflection layers are disposed symmetrically about the active layer.   
     
     
         10 . The transmissive image modulator of  claim 9 ,
 wherein a reflectance of the first lower reflection layer is the same as a reflectance of the second upper reflection layer, and a reflectance of the second lower reflection layer is the same as a reflectance of the first upper reflection layer.   
     
     
         11 . The transmissive image modulator of  claim 6 ,
 wherein a phase of light reflected at the surface of the second upper reflection layer lags by π, while phases of light reflected at surfaces of the first lower reflection layer, the second lower reflection layer, and the first upper reflection layer are 0.   
     
     
         12 . The transmissive image modulator of  claim 2 ,
 wherein the first refractive index layer is made from Al x Ga 1-x As, and the second refractive index layer is made from Al y Ga 1-y AS, where 0<x<1, 0<y<1, and x<y.   
     
     
         13 . The transmissive image modulator of  claim 1 ,
 wherein the active layer comprises the plurality of quantum well layers and the plurality of barrier layers stacked alternately, a first cladding layer disposed between the lower reflection layer and the active layer, and a second cladding layer disposed between the upper reflection layer and the active layer.   
     
     
         14 . The transmissive image modulator of  claim 13 ,
 wherein a refractive index of the first cladding layer is between a refractive index of the quantum well layer and a refractive index of the upper reflection layer,   a refractive index of the second cladding layer is between a refractive index of the quantum well layer and a refractive index of the lower reflection layer, and   the first cladding layer and the second cladding layer are made from the same material and have the same thickness.   
     
     
         15 . The transmissive image modulator of  claim 13 ,
 wherein the multiple quantum well layer comprises first quantum well layers and second quantum well layers, wherein a thickness of the first quantum well layers is different from a thickness of the second quantum well layers.   
     
     
         16 . The transmissive image modulator of  claim 1 ,
 further comprising, a first contact layer disposed on a lower surface of the lower reflection layer, and a second contact layer disposed on a top layer of the upper reflection layer.   
     
     
         17 . The transmissive image modulator of  claim 16 ,
 wherein the first contact layer is made from n-GaAs or n-InGaP.   
     
     
         18 . The transmissive image modulator of  claim 16 ,
 further comprising, a substrate disposed on the lower surface of the first contact layer, and a transparent widow formed in a center of the substrate by removing a central part of the substrate.   
     
     
         19 . The transmissive image modulator of  claim 18 ,
 further comprising, a transparent resin applied to the second contact layer, and a transparent cover disposed on the transparent resin.   
     
     
         20 . A method of forming a transmissive image modulator on a substrate, the method comprising,
 forming a first contact layer on a substrate;   forming the transmissive image modulator on the first contact layer, wherein the transmissive image modulator comprises:
 a lower reflection layer, 
 an active layer disposed on the lower reflection layer, the active layer comprising a plurality of quantum well layers and a plurality of barrier layers, and 
 an upper reflection layer disposed on the active layer, 
 wherein the lower reflection layer comprises at least one first micro-cavity layer disposed therein. 
 wherein the upper reflection layer comprises at least one second micro-cavity layer disposed therein, and 
 wherein the active layer has a thickness which is a multiple of λ/2, the at least one first micro-cavity layer has a thickness which is a multiple of λ/2, and the at least one second micro-cavity layer has a thickness which is a multiple of λ/2, where λ is a resonant wavelength; 
   forming a second contact layer on a top surface of the upper reflection layer; and   forming a transparent window by removing a central part of the substrate.   
     
     
         21 . The method of  claim 20 ,
 wherein the first contact layer is made from n-GaAs, the forming the first contact layer on the substrate comprises forming an AlAs buffer layer on the substrate, and forming the first contact layer on the AlAs buffer layer.   
     
     
         22 . The method of  claim 21 ,
 wherein the forming the transparent window by removing the central part of the substrate comprises:
 forming a first protection layer on a bottom surface of the substrate and forming a second protection layer on a top surface of the second contact layer; 
 forming a photoresist layer along an edge of the first protection layer, and removing a central part of the first protection layer to expose the substrate; 
 removing a portion of the exposed substrate with a dry etching; 
 removing a remaining part of the exposed substrate with a wet etching, this exposing the buffer layer; and 
 removing the exposed buffer layer and the first protection layer and the second protection layer. 
   
     
     
         23 . The method of  claim 20 ,
 wherein the first contact layer is made from n-InGaP.   
     
     
         24 . The method of  claim 23 ,
 wherein the forming the transparent window by removing the central part of the substrate comprises:
 forming a first protection layer on a bottom surface of the substrate and forming a second protection layer on a top surface of the second contact layer; 
 forming a photoresist layer along an edge of the first protection layer, and removing a central part of the first protection layer to expose the substrate; 
 removing an exposed part of the substrate with a wet etching method to expose the buffer layer; and 
 removing the exposed buffer layer and the first and second protection layers.